Circuit board with quality-indicator mark and method for indicating quality of the circuit board

A circuit board with a quality-indicator mark, comprising:

• a plurality of circuit board units each having a multi-layer circuit structure;
• at least one conductive mark formed on a surface of each of the circuit board units;
• and
• a plating bus formed around each of the circuit board units, wherein the plating bus is electrically connected to the circuit structure of each of the circuit board units and is selectively electrically connected to the conductive mark via a plating trace formed in an inner-layer circuit structure of the circuit board unit and via interconnections in the circuit board unit,
• wherein a metal protective layer is formed on the conductive mark via the plating bus so that existence of the metal protective layer on the conductive mark shows a closed circuit between the plating trace formed in the inner-layer circuit structure and the plating bus, the circuit board unit includes a core and at least one build-up circuit layer formed respectively on front and back surfaces of the core, a conductive via is formned at a terminal of the plating trace, and the conductive mark is formed on the conductive via and located at the build-up circuit layer.